Through silicon vias (TSV) are used for a number of applications, including low inductance ground connections for RF devices. Typically, TSVs are filled with either tungsten or copper, which are electrically insulated from the substrate. In such processes, the substrate is insulated from the tungsten using a TiN liner, in order to avoid degradation of the silicon within the TSV. Degradation, of the silicon, is known to lead to cracking and reduced fracture strength of the substrate.
Tungsten filled TSVs have a number of advantages compared to copper filled TSVs. For example, tungsten can be deposited by chemical vapor deposition (CVD), so it is easy to fill high aspect ratio vias. However, a disadvantage of tungsten compared to copper is that the elastic modulus is high. The high elastic modulus, in turn, results in a higher stress in the silicon for tungsten filled TSV verses copper filled TSV. Hence there is a higher risk of wafer cracking and die cracking for tungsten filled TSV than copper filled TSV.
FIG. 1, for example, shows the fracture strength of wafers in different configurations. More specifically, FIG. 1 shows the fracture strength of a silicon wafer without a TSV, and during additional processes. For example, the fracture strength shown at point “A” is representative of a silicon wafer without a TSV. On the other hand, point “B” is representative of the fracture strength of the wafer with a TSV etched into the substrate. As shown, point “B” exhibits an approximate 50% reduction in strength compared to a silicon wafer without a TSV. Points “C”, “D” and “E” represent the fracture strength of the wafer post fill with tungsten. Here, again, the fracture strength at points “C”, “D” and “E” is lower than even point “B”. The wafer again regains some strength after it is thinned, as shown at point “F”. Although the wafer regains some fracture strength, it never exhibits the same strength as shown at point “A”, and barely greater than that at point “B”. Accordingly, it is shown in this graph that fracture strength is greatly reduced by having a TSV, and even further reduced by using conventional tungsten fill processes.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.